Expectations vs. Reality: The Subtle Reasons Why Tomorrow's Snowstorm Isn't The Big Snowmageddon We Once Thought

Credit: NBC12 News Richmond

Seems old man winter still has alot to say as Richmond prepares for its next wintry chapter tomorrow. Indeed, it appears the city is poised to see another round of the beloved (or dreaded) "S" word with the metro area expecting a solid 3-6 inches of snow. Farther south and east, however, 6+ inches of snow appears likely with the Virginia Beach area in the crosshairs for locally higher amounts. But wait a minute...I thought a week ago we were expecting some 6-12 inches of snow in the metro?

How is it that the flakes of fun ended up leaving the (804) to take the party to the (757)? 

January 10, 2025 Snowstorm

        As a snow lover, I was giddy at the potential for the "big one"! Richmond has been long overdue for a 6+ inch event and I talked about the snow drought Richmond had been under for the past almost 3 years in a previous blog. That snow drought has thankfully come to an end and the metro has seen a fair number of wintry events this season so far. 

        But alas, the big Snowmageddon remained elusive....until last week. The early hints of its wake up from hibernation first appeared roughly a week ago, with some impressive model signals for a bigtime snow event. Both the GFS and Euro        models appeared to be on board with the idea of a an ideal "coastal rider" setup, which would put the metro area right in the bullseye for some heavy snowfall. But as is always the case, things were subject to change and unfortunately, it did not change in a favorable direction for metro snowlovers. 

        So what happened? How did we go from at one point 6-12+ inches to only 3-6 inches forecasted now? Well...I have a couple of theories that point to why it can be incredibly difficult to land the "sweet spot" for snow in the metro region. I'll discuss in more detail below why I believe a less favorable upper wind pattern 

Troubles in the Upper Levels... 

One interesting observation I've had over the last day or so of looking over the model guidance is a less favorable upper level wind pattern. Broadly speaking, in order for robust area of low pressure to form and bring us our storm, you look two different things: a trough or "dip" in the winds aloft and the creation of "divergence" aloft from the fast wind speeds, which will lead to a vacuum like effect that draws air upwards and outwards. 

To invigorate the development and strengthening of the area of low pressure along the coast, you would want the orientation of the winds aloft to be more south-southwesterly and more parallel to the coast. Ideally, you'd also look for a strong trough that takes on a neutral or negative tilt, which would provide more divergence aloft and would potentially lead to the development of a stronger surface low (although positive tilts can still work too). 

If you look at Figure 1 below, however, you can see that while there is some degree of southwesterly flow aloft by Wednesday afternoon, the general flow has more of a "west to east" (zonal) flow to it. In addition, you'll notice that the upper level trough has a more "positive" slope, which is what leads to a slightly more west to east component and a less vigorous environment for a robust surface low development. 

Figure 1: 500 mlb Winds (Mid Level). As seen here, the winds across the Virginia at 1 PM on Wednesday have a more west-east component to them rather than a true south-southwest orientation. In addition, as highlighted in the black bar above, the 

Eventually as Wednesday rolls into Thursday, the trough begins to take on a more robust "neutral" tilt and strengthens...but this happens too late when the storm has already exited the region (Figure 2). 

Figure 2: 500 mlb winds for Thursday at 7 am. Notice the more "neutral" tilt of the tough axis and more south-southwesterly wind components over Virginia. This happens too late after this system is pulling away

So what's the big deal? The tilt, timing, and directional component of the upper level wind field for this system presents challenges. For one, the more optimal tilt angle comes in too late. Secondly, the more westerly component of the upper wind field drives the low pressure further south and east, leading to southerly storm track and a quicker exit from the region. In other words, the upper level wind pattern supports a storm that is shunted southward, slightly too far off the coast, and a storm that exits too quickly.    

Those Darn Canadians... 

Another issue I see is the sharp cutoff of snow precipitation due to the very dry, cold air originating from Canada. Unlike previous events, this snow event will have plenty of cold air to work with. However, this air is rather dry and this might lead to a sharp gradient on the NW side of the metro that could reduce snow totals. Even by Wednesday night, dewpoints only rise into the low 20s (Figure 3). While air temps will remains in the 20s during the night, leading to saturation, this dry air could lead to sharper snow total gradients. 

Figure 3: A Forecasted Skew-T Sounding For The Richmond Area. The circled area highlights the temperature (red line) and dewpoint (green line). While the temperature and dewpoints are close (ie fully saturated air), the dewpoint is only 22 degrees, indicating a pretty dry airmass.